1. Field of the Invention
The present invention relates to a speaker array system having a speaker array comprised of speaker units for emitting an acoustic beam.
2. Description of the Related Art
As a speaker array system of this type, there is a speaker array system of delay array type (see, for example, paragraph 0004 and FIG. 9 of Japanese Laid-open Patent Publication No. 2006-109343). In such a speaker array system of delay array type, delay amounts of audio signals supplied to speaker units of a speaker array are adjusted for control of a sound field and a directivity characteristic of acoustic waves emitted from the speaker array. For example, delays determined based on differences between paths extending from a virtual acoustic center to the speaker units are applied to the audio signals for the speaker units, whereby sound can be reproduced as if it were emitted isotropically from an acoustic source at the virtual acoustic center and spread out in a spherical wave.
FIG. 15 shows how acoustic waves (hereinafter referred to as wavelets), which are output from the speaker units of the speaker array system of delay array type are superposed on one another. In FIG. 15, rmin represents the length of a path from an acoustic center to an uppermost speaker, ri represents the length of a path from the acoustic center to a lowermost speaker, and a path difference ri-rmin corresponds to a delay. With the speaker array system of delay array type, the dense degree of wavelet superposition varies depending on directions of acoustic wave propagation, as shown in FIG. 15. The sound pressure becomes higher at a place where the wavelets are more densely superposed on one another. With the speaker array system of delay array type, therefore, the strength of sound listened to by an audience varies in dependence on a positional relation between the audience and the speaker array. Thus, the speaker array system of delay array type has a drawback that it cannot realize an acoustic service that provides nearly uniform sound volume to any area having arbitrary shape and size (i.e., emission of an acoustic beam that produces sound listenable to at a nearly uniform sound volume in any position in the area).